1. Field of the Invention
This invention relates to the use of aminoalkanolamide esters of carboxylic acids as processing aids for thermoplastics.
2. Discussion of Background Art
Processing aids have to be used in the processing of thermoplastics to promote melting and the formation of a homogeneous fluid melt and to facilitate the flow of the melt by reducing internal friction. This can be achieved by addition of lubricants which are added to the thermoplastic before processing. On the other hand, it is important in the processing of thermoplastics to prevent the plastic melt from adhering to hot surfaces of the machine or to the walls of the molds. Mold release agents are used for this purpose, migrating from the plastic to the surface after incorporation on account of their only limited compatibility and thus reducing adhesion. Both here and in the following, the term "mold release agent" is used synonymously for the term "external lubricant" normally used, particularly in the field of PVC. In principle, the use of processing aids also has a major influence on the morphology, homogeneity and surface quality of the plastic products.
Whether an additive acts as a lubricant or mold release agent depends on many factors, including its structure and also the type and plastic material in question, the lubricating effect and the mold release effect often being developed at one and the same time. Metal soaps, fatty acid esters and fatty acid amides are generally used as lubricants for relatively apolar plastics, such as polyethylenes and polypropylenes. Relatively polar plastics, such as polyesters, polycarbonates, polyamides, PVC, polystyrene and ABS, generally need both lubricants and mold release agents. Suitable mold release agents are fatty acid amides, metal soaps, polyethylene waxes, fatty acid esters or even silicone oil which, in general, is externally applied. Suitable internal lubricants for polar plastics divided into chemical classes are listed in Ullmanns Encyklop adie der technischen Chemie, 4th Revised and Extended Edition, Vol. 15, Verlag Chemie, Weinheim, 1978, pages 568-569 and in G achter/M uller, Kunststoffadditive, 3rd Edition, Carl Hanser Verlag, 1990, pages 443-505.
However, known mold release agents in particular, which are mainly of importance in the processing of thermoplastics by injection molding, have one disadvantage. In injection molding, hot plastic melts are forced into a metal mold in which they cool until they can be ejected with under light pressure. With known mold release agents, a long cooling phase had to be accepted. Thus, the mold release agents only developed their full release effect at low demolding temperatures. For economic reasons, therefore, ideal mold release agents should develop a release effect at high temperatures and should enable moldings to be ejected under light ejector pressure. Known lubricants are also in need of improvement in regard to their ability to form a homogeneous fluid melt so that even complicated structures can be produced from thermoplastics, above all from polyamides, olefins and also polystyrene and copolymers (for example ABS, ASA). In addition, the processing aid should not in any way affect the color or molding behavior of the thermoplastic during processing and should be substantially non-volatile and heat-stable.
The problem addressed by the present invention was to provide processing aids which would satisfy these requirements.